1. Field of the Invention
The invention relates to combustion chambers for gas turbine engines, particularly to an annular combustion chamber.
2. The Prior Art
U.S. Pat. No. 2,693,676 and German Pat. No. DT-AS 10 79 895 disclose gas turbine engine combustion chambers having T-shaped vaporizer tubes which project into the combustion space of the combustion chamber.
In both disclosures, the respective two outer ends of the vaporizer cross tubes are bent at 90.degree. relative to a longitudinal centerline of the cross tube such that the two outlet ports of each vaporizer are directed towards the back wall of the flame tube.
In this arrangement, the fuel-air mixture flowing in the direction of the flame tube is enriched with primary air forced into the flame tube or the primary zone in a direction countering the flow of the fuel-air mixture. The air is provided by means of air nozzles arranged in the back wall.
In these two disclosures, then, the primary zone eddies, which partially consist of fuel-air components in concentrated gaseous form, will essentially develop only in the area between the flame tube back wall and the vaporizer outlet ports facing said back wall.
In practice it has been shown, however, that the relatively small primary zone eddies developing in the manner just described will not give the stability of flame required in modern gas turbine engines as a result of the relatively high process temperatures and the attending relatively high air-fuel flows and primary air influx velocities.
It has also been shown that combustion chambers of this type, having T-shaped fuel vaporizers, will not adequately permit propagation of a uniform, rotationally symmetrical flame front to be achieved in the interest of a maximally uniform high temperature load and combustion efficiency.
In addition, the vaporizers described above are inherently limited by their inability to vaporize more than 8% to 10% of the incoming fuel.
Considering the high process temperatures at relatively elevated turbine inlet temperatures of about 1300.degree. K. and above which are required for modern gas turbine engines and especially for turbojet engines, fuel vaporization rate achieved with the aid of the above described vaporizers is insufficient to adequately condition the incoming fuel-air mixture for homogeneous, stable combustion.
It should also be noted that such vaporizers are able to handle relatively low fuel-air flows as a result of their design and as a result of the fact that the velocity of the respective combustion air flow that can be handled will essentially remain constant.
A further disadvantage affecting such vaporizers is that fuel tends to carbonize, especially in the bends of the 90-degree angle ends of the vaporizer cross tubes. Apart from the undesirable carbon formed in this manner, engine damage may also be caused, e.g. when carbon deposited at said bends comes loose as a result of certain natural vibrations of these vaporizers.